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International Conference on Laser, Optics and Optoelectronic Technology (LOPET)

Experimental research on continuous variable quantum key distribution in fiber channel

GuiBao Dai, Qing Pan, Jianru Li, Yani Zhang, Ying Liu

Published Jun 24, 2021• 0 citations
Publisher

Abstract

The use of quantum key distribution for encryption to realize the secure transmission of information is a research hotspot in the field of secure communication. In theory, it has a high degree of security with quantum mechanics as a guarantee. In particular, continuous variable quantum key distribution has the advantages of simple quantum state preparation, relatively high key rate and low detector cost, so it has attracted wide attention from all over the world. However, the continuous variable quantum key distribution will be affected by factors such as fiber type and fiber attenuation when it is transmitted in the fiber channel. Therefore, a large number of experimental tests must be carried out in the fiber channel before the quantum key distribution device is connected to the optical network. Therefore, this paper conducted continuous quantum key distribution experiments in different lengths of terrestrial optical fiber G.652D and submarine optical fiber G.654D. Among them, the quantum key generation rate reaches an average of 10kbit/s, and the quantum error rate is within 10%. As the distance increases, the variance of the transmission coefficient and the shot noise becomes smaller and the amplitude of the excess noise fluctuation becomes larger. The negotiation efficiency is above 92.44%. The experimental results show that continuous quantum key distribution has good compatibility in both G.652D and G.654D fibers. The experimental data provides a large amount of data support for subsequent research on the access of quantum key distribution equipment to optical networks.

DOI
10.1117/12.2602642

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The use of quantum key distribution for encryption to realize the secure transmission of information is a research hotspot in the field of secure communication. In theory, it has a high degree of security with quantum mechanics as a guarantee. In particular, continuous variable quantum key distribution has the advantages of simple quantum state preparation, relatively high key rate and low detector cost, so it has attracted wide attention from all over the world. However, the continuous variable quantum key distribution will be affected by factors such as fiber type and fiber attenuation when it is transmitted in the fiber channel. Therefore, a large number of experimental tests must be carried out in the fiber channel before the quantum key distribution device is connected to the optical network. Therefore, this paper conducted continuous quantum key distribution experiments in different lengths of terrestrial optical fiber G.652D and submarine optical fiber G.654D. Among them, the quantum key generation rate reaches an average of 10kbit/s, and the quantum error rate is within 10%. As the distance increases, the variance of the transmission coefficient and the shot noise becomes smaller and the amplitude of the excess noise fluctuation becomes larger. The negotiation efficiency is above 92.44%. The experimental results show that continuous quantum key distribution has good compatibility in both G.652D and G.654D fibers. The experimental data provides a large amount of data support for subsequent research on the access of quantum key distribution equipment to optical networks.
Quantum key distribution (QKD) enables two remote parties to share encryption keys with security based on the laws of physics. Continuous-variable (CV) QKD with coherent states and coherent detection integrates well with existing telecommunication networks. Thus far, long-distance CV-QKD has only been demonstrated using a highly complex scheme where the local oscillator is transmitted, opening security loopholes for eavesdroppers and limiting potential applications. Here, we report a long-distance CV-QKD experiment with a locally generated local oscillator over a 100-kilometer fiber channel with a total loss of 15.4 decibels. This record-breaking distance is achieved by controlling the phase noise-induced excess noise through a machine learning framework for carrier recovery and optimizing the modulation variance. We implement the full CV-QKD protocol and demonstrate the generation of keys secure against collective attacks in the finite-size regime. Our results mark a substantial milestone for realizing CV quantum access networks with a high loss budget and pave the way for large-scale deployment of secure QKD.
Quantum key distribution provides secure keys resistant to code-breaking quantum computers. The continuous-variable version of quantum key distribution offers the advantages of higher secret key rates in metropolitan areas, as well as the use of standard telecom components that can operate at room temperature. However, the transmission distance of these systems (compared with discrete-variable systems) are currently limited and considered unsuitable for long-distance distribution. Herein, we report the experimental results of long distance continuous-variable quantum key distribution over 202.81 km of ultralow-loss optical fiber by suitably controlling the excess noise and employing highly efficient reconciliation procedures. This record-breaking implementation of the continuous-variable quantum key distribution doubles the previous distance record and shows the road for long-distance and large-scale secure quantum key distribution using room-temperature standard telecom components.
Quantum key distribution with continuous variables already uses advantageous high-speed single-mode homodyne detection with low electronic noise at room temperature. Together with continuous-variable information encoding to nonclassical states, the distance for secure key transmission through lossy channels can approach 300 km in current optical fibers. Such protocols tolerate higher channel noise and also limited data processing efficiency compared to coherent-state protocols. The secret key rate can be further increased by increasing the system clock rates, and, further, by a suitable frequency-mode-multiplexing of optical transmission channels. However, the multiplexed modes couple together in the source or any other part of the protocol. Therefore, multiplexed communication will experience cross talk and the gain can be minuscule. Advantageously, homodyne detectors allow solving this cross-talk problem by proper data processing. It is a potential advantage over protocols with single-photon detectors, which do not enable similar data processing techniques. We demonstrate the positive outcome of this methodology on the experimentally characterized frequency-multiplexed entangled source of femtosecond optical pulses with natural cross talk between eight entangled pairs of modes. As the main result, we predict the almost 15-fold higher secret key rate. This experimental test and analysis of frequency-multiplexed entanglement source open the way for the field implementation of high-capacity quantum key distribution with continuous variables.
Quantum key distribution is the first major area of quantum information science to find practical use outside of its field. Quantum key distribution involves transmitting cryptographic keys using quantum states. Any attempt to eavesdrop on the transmission will, necessarily by the laws of quantum mechanics, disturb or destroy the states. By identifying and only using keys that have not been disturbed, a perfectly secure cryptographic system can be realised. ¶ Discrete variable quantum key distribution was proposed in 1984. Since then attempts to exploit this technology have been beset with the difficulties of working with the discrete variables in question—single photon states. In the late 90’s the idea of continuous variable quantum key distribution was developed, in which the key-carrying quantum information states are properties of a bright, continuous wave laser beam. Bright laser beams are relatively simple to manipulate and can carry large amounts of information even when subject to high loss. ‘Broadband’ continuous variable quantum key distribution refers to the large information rates obtainable by using broad laser modulation sidebands. ¶ In 2005 the ANU Quantum Optics group published an experimental demonstration of broadband continuous variable quantum key distribution. This thesis documents the project work undertaken to rebuild an improved version of this experiment, and also the work undertaken to prepare for more advanced experiments. The main goal of the improved experiment was to increase the key distribution rate, while the advanced experiments were directed towards practical implementation of the system in optical fibre. ¶ The experiment rebuild was achieved with most improvements for higher bandwidth successfully implemented. Some improvements were unplanned, being necessitated by problems with the initial improvements. Although preliminary experimental data was acquired, time constraints precluded a successful cryptographic key distribution. Pilot design and major purchasing for future experiments was also completed.
Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have been demonstrated only indoors or over short outdoor distances. Here, by developing channel-fluctuation-independent high-precision manipulation of continuous-variable quantum states, high-accuracy quantum signal acquisition and processing, and high-efficiency free-space acquisition, tracking, and pointing technology, we overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and narrow-linewidth spectral filtering and demonstrate for the first time long-distance free-space quantum key distribution under the asymptotic condition over 7-km inland and 9.6-km maritime atmospheric channels with Gaussian-modulated coherent states. Given that the CVQKD system is naturally compatible with existing ground fiber telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications.
Abstract Quantum key distribution (QKD) can offer communication with unconditional security and is a promising technology to protect next generation communication systems. For QKD to see commercial success, several key challenges have to be solved, such as integrating QKD signals into existing fiber optical networks. In this paper, we present experimental verification of QKD co-propagating with a large number of wavelength division multiplexing (WDM) coherent data channels. We show successful secret key generation over 24 h for a continuous-variable QKD channel jointly transmitted with 100 WDM channels of erbium doped fiber amplified polarization multiplexed 16-ary quadrature amplitude modulation signals amounting to a datarate of 18.3 Tbit/s. Compared to previous co-propagation results in the C-band, we demonstrate more than a factor of 10 increase in the number of WDM channels and more than 90 times higher classical bitrate, showing the co-propagation with Tbit/s data-carrying channels.